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Herbs and Supplements to Use Only With Caution

In hypothyroidism, the thyroid gland fails to produce adequate levels of thyroid hormone. Symptoms include the following:

Sluggishness

Sensitivity to cold

Weight gain

Depression

Dry skin

Loss of hair

Excessive menstruation

Hoarseness

Goiter (a visible enlargement of the neck caused by a swollen thyroid gland)

Hashimoto’s thyroiditis is the most common natural cause of low thyroid hormone levels. In this autoimmune condition, the body develops antibodies that attack and gradually destroy the thyroid. A viral infection of the thyroid can also decrease thyroid hormone production, but the effect is generally mild and temporary. Finally,
iodine
deficiency can cause hypothyroidism, but this seldom occurs in the developed world where iodine is routinely added to salt.

Besides these natural causes, there is a still more common cause of hypothyroidism—medical treatment for
hyper
thyroidism
(excessive production of thyroid hormone production). People with certain forms of hyperthyroidism receive treatment with radioactive iodine to inactivate the thyroid gland. This treatment causes hypothyroidism, which requires lifelong treatment with thyroid replacement therapy.

Until the 1990s, doctors commonly diagnosed hypothyroidism by conducting lab tests to measure thyroid hormone levels in the blood (the T
4
level). Unfortunately, normal thyroid levels vary widely between people, so this method couldn’t always correctly identify the disease. A much better lab test, which became available in the 1990s, involves measurement of a hormone called TSH, or thyroid stimulating hormone.

TSH is released by the pituitary gland in order to control the thyroid gland. The pituitary gland constantly measures the level of thyroid hormone in the blood and adjusts TSH levels as necessary to get it right. When thyroid hormone levels are high, it turns TSH levels down. When thyroid hormone levels are too low, the pituitary raises TSH levels to stimulate the thyroid. If the thyroid gland does not respond by raising thyroid hormone levels, the pituitary turns up the TSH levels even higher. When TSH levels are higher than normal limits, this means that the thyroid gland is having trouble producing enough thyroid hormone for the body’s needs: in other words, the person has entered a hypothyroid state, or is about to enter such a state. This method of determining thyroid status has proved very reliable. In other words, the pituitary gland knows what it is talking about.

Medical treatment for low-thyroid conditions is safe and very effective. Treatment involves use of a hormone called levothyroxine, or T
4
. The body actually uses two forms of thyroid, T
4
and T
3
, but in most cases the body easily and automatically converts T
4
to T
3
in the right proportions. The dosage of drug is adjusted by monitoring TSH levels. When the pituitary gland is satisfied, the dose is most likely correct.

Other Proposed Treatments

So-called natural thyroid hormone is popular among people interested in alternative medicine. Sold by prescription under different brand names, this extract of pig (or mixed pork and beef) thyroid contains both T
4
and T
3
(see previous section for description). There is no doubt that extract is as effective as standard synthetic thyroid hormone, and it is a satisfactory choice for those who prefer to use natural treatments. However, there is no evidence that extract is any more effective than standard medications, and there are some concerns that variations in stomach absorption may produce slightly erratic results.

One double-blind study failed to find a combination of synthetic T
3
and T
4
more effective than synthetic T
4
as a treatment for hypothyroidism in regard to well-being, quality of life, or mental function.
18
Another double-blind study failed to find any difference between T
4
alone or T
3
plus T
4
in people whose thyroid had been removed because of thyroid cancer.
20
Yet another study also failed to find discernible differences between the two treatments regarding mood, fatigue, well-being, or mental function; however, for reasons that are unclear, patients given T
3
plus T
4
were significantly more likely to prefer the new treatment to their previous care than those who were continued on T
4
.
19
Unless this was merely a statistical accident, people were apparently able to detect some subtle benefit with the combined treatment that they could not quite put their finger on.

Selenium
, though, may offer some benefits.
21
A review of 6 randomized trials, involving 339 people with hypothyroidism, compared selenium (200 mcg daily for 3 months) to placebo. Those in the selenium group reported improvements in their mood and well-being, and lab tests found lower levels of the antibodies that attack the thyroid.

Far too frequently, people with low thyroid levels consume seaweed or
iodine
supplements in hopes that they will help. However, while iodine deficiency does indeed cause low thyroid levels, taking iodine will not help at all if you are not deficient in it, and the vast majority of people living in the developed world have plenty of iodine. In fact, excessive iodine intake can occasionally cause hypothyroidism. This is a classic case of “more is not better.” (For more information, see
Herbs and Supplements to Use Only With Caution
below.)

The Theory of Widespread Marginal Hypothyroidism

There is very little doubt that many cases of marginal hypothyroidism go unidentified, and that occasional tests for thyroid adequacy should be part of routine medical care. However, some proponents of alternative medicine go further and suggest that undiagnosed hypothyroidism is a serious epidemic, causing a high percentage of all the illnesses afflicting modern man. (One of the most famous books on this theory is titled
Solved: The Riddle of Illness
by Stephen E. Langer, MD, and James F. Scheer.) Supposedly, laboratory tests for thyroid hormone levels are not reliable, and many people have marginally low thyroid levels despite normal lab readings.

These thyroid enthusiasts recommend that people use measurements of basal body temperature and not blood tests to determine whether thyroid levels are adequate. Basal body temperature is measured by placing a thermometer under the armpit before arising in the morning. According to proponents of the marginal hypothyroidism theory, a measurement of lower than about 97.5°F indicates a problem. People with basal body temperature readings below this level and symptoms consistent with hypothyroidism are advised to use animal-source thyroid gland supplements, which can be obtained with a bit of work. The net result is supposed to be a great improvement in overall health and the resolution of many illnesses.

However, there are a number of problems with this theory. One is that the majority of women have basal body temperature readings below 97.5°F in the period prior to ovulation, a fact used in the sympto-thermal method of natural family planning. Many healthy men have normal basal body temperatures below 97.5°F as well. Since symptoms consistent with hypothyroidism (such as, fatigue, depression, weight gain) occur in a great many people, this approach is guaranteed to recommend that enormous numbers of people take thyroid supplements.

Furthermore, the basal body temperature method was developed in the days before TSH levels could be measured. Back then, doctors could only measure T
4
levels, and as noted above, there is too great a variation in the normal level of T
4
for such tests to be reliable. However, now that the TSH test has become available, the situation has changed. TSH measurements indicate the body’s own determination of its thyroid hormone level. It is difficult to justify ignoring the body’s own opinion in favor of an arbitrary reading on a thermometer. Indeed, when people with normal TSH levels are given thyroid medication, the body responds by lowering its own production of thyroid hormone, essentially fighting this supposedly natural therapy.

Nonetheless, the enthusiasm for thyroid medication continues unabated, and some alternative medicine physicians continue to maintain that thyroid hormone supplementation is useful even in the presence of a normal TSH test. In 2001, a
double-blind, placebo-controlled, crossover trial
attempted to evaluate the validity of this theory.
1
Researchers enrolled 22 people with symptoms consistent with hypothyroidism but normal TSH measurements, as well as 19 healthy people. About half of each group was given standard synthetic thyroid hormone (thyroxine 100 mcg—this is T
4
as described above) for 12 weeks and placebo for another 12 weeks; the other half received placebo for the first period and thyroid hormone for the second. Improvement was measured through questionnaires evaluating general health, emotional well-being, and mental function.

The results showed that participants with symptoms of low thyroid hormone improved significantly. However, those taking placebo improved just as much! In other words, thyroid hormone proved no more effective than placebo. (Interestingly, the healthy participants showed little response to either placebo or thyroid hormone.)

This study indicates that synthetic human thyroid hormone supplementation (T
4
) is not helpful for people with normal TSH but with symptoms that are reminiscent of low thyroid hormone. Unfortunately, it did not evaluate the effectiveness of the animal-source thyroid recommended by proponents of the hypothyroid theory, and therefore, does not entirely settle the controversy.

Herbs and Supplements to Use Only With Caution

As noted above, supplementation with iodine will not help the thyroid gland except in people who are iodine-deficient. In fact, in Japan, excessive use of seaweed (such as
kelp
or
bladderwrack
) is a fairly common cause of hypothyroidism.
2-5

For this reason, people with low thyroid hormone levels should not consume excessive amounts of these iodine-rich foods.

Soy
and its
isoflavones
(such as
genistein
) appear to have numerous potential effects involving the thyroid gland. When given to people with impaired thyroid function, soy products have been observed to reduce absorption of thyroid medication.
6-8
In addition, some evidence hints that soy isoflavones may directly inhibit the function of the thyroid gland, although this inhibition may only be significant in people who are deficient in iodine.
9-11
However, to make matters more confusing, studies of healthy humans and animals given soy isoflavones or other soy products have generally found that soy either had no effect on thyroid hormone levels, or actually increased levels.
12-16

The bottom line:
In view of soy’s complex effects regarding the thyroid, people with impaired thyroid function should not take large amounts of soy products except under the supervision of a physician.

Iron
supplements may also interfere with thyroid hormone absorption.
17

Revision Information

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.

Yamaguchi K, Fukushima H, Uzawa H, et al. A case of iodide myxedema observed for three years under a low iodide diet—especially on the restoration of the escape mechanism from the Wolff-Chaikoff effect.
Nippon Naibunpi Gakkai Zasshi
. 1984;60:79-88.